A platen press is heated by heating elements that are built into the press platens. Heating capsules, normally of an automatically self-temperature-stabilizing PTC ceramic whose resistance increases as its temperature rises to a predetermined level, are mounted in the platen. Conductors are connected to the ends of these capsules so that electricity can be passed through them to energize them. Typically separate ceramic or ceramic-lined seats are provided for the capsules, and separate conductors for the requisite electrical connections are required.
Such construction is relatively complex and difficult. In addition such a heating element is extremely susceptible to damage by moisture. Any moisture that gets into the heating element will quickly create corrosion due to the high temperature and presence of electricity. In fact such platens have a woefully short service life whenever employed in wet environments, or when used to press objects that generate steam when pressed, as for instant in a belt-manufacturing or -repair press.
The same problems also mitigate against any use of this type of heater in a household appliance, as such a heater is useless if it cannot be used where steam is generated and or if it cannot be thoroughly washed.
Another difficulty with this type of heating element is that replacing it is an onerous job. In fact if the heating element incorporated in a heater such as a platen press fails it is necessary to disassemble the heater and do extensive complex work to replace even a small portion of the heating element, much less all of it. The down time for such repair in an industrial application is considerable.